To support increases in the capacity of magnetic disk drives, magnetic recording media that are capable of recording data in higher planar densities are needed. While a high planar recording density is generally not achievable with some types of magnetic recording systems, perpendicular recording systems may provide such improvement.
Perpendicular recording systems record bits formed by a magnetic field in a direction that is perpendicular to the plane of a perpendicular magnetic recording medium having perpendicular magnetizing anisotropy, with adjacent bits being magnetized in the anti-parallel direction. The magnetic moments of adjacent bits stabilize each other, which allows an increase in coercive force and therefore contributes to high-density recording.
A conventional perpendicular magnetic recording medium is made up of a thick soft magnetic film (i.e., a soft underlayer) having a high permeability and a perpendicular recording layer having a high perpendicular anisotropy, typically separated by a spacer layer. One problem with the highly permeable, thick soft underlayer is that it is susceptible to the formation of domain walls, which produce noise at the time of recording and therefore adversely affects reproduction of data from the medium. The noise degrades the quality of readback data. Another problem is manufacturing cost. Typically, the soft underlayer material is applied to the substrate by a low-rate sputtering process. Because of the thickness of the material, the sputtering process can be time-consuming and therefore can be quite costly.